Brake Systems 101

One of the most under-appreciated systems in a car is the brake system. Or, at least, usually under-appreciated. When you suddenly need to slam on the brakes in traffic, you’re definitely appreciating the job your brakes do.

Most people have a vague idea of how their vehicle’s brakes work, and probably know a little bit about brake pads. But the brake system as a whole is a complicated mechanism that most don’t really understand. Getting a better idea of how a vehicle’s brakes work and what to be on the lookout for in terms of performance is an important part of becoming a more knowledgeable and safe driver.

The Basics

When your car is traveling, that’s a large amount of energy in motion. In order to stop the car, it’s necessary to get rid of that energy.  Scientifically speaking, the basic concept of a car’s braking system is a method to remove the kinetic energy (energy of motion) to slow or stop your vehicle. Or, more accurately stated if you remember a physics class you might have taken in high school or college, the energy has to be converted because it doesn’t technically go away. Car brakes get rid of the energy of motion by converting it to heat through the use of friction.

Modern brake systems are hydraulic. This means they operate using fluid to do their job. The brake system starts with the brake pedal you press, extends to a pushrod that pushes a piston in the brake master cylinder. The piston forces hydraulic fluid into a series of metal lines (pipes) and hoses, which ultimately applies pressure to a brake caliper or brake wheel cylinder assembly ending with either brake pads squeezing brake discs or brake shoes expanding against brake drums.

That very end of the process is where the friction is generated by the system to stop the car. The middle part acts as a force multiplier; channeling the force you push onto the brake pedal with your foot and magnifying it exponentially.

You don’t necessarily need to know all the nuts and bolts of how the braking system works, but it’s good to understand the basic idea. It’s also a good idea to understand the difference between the two main types of brakes – Disc Brakes and Drum Brakes.

Disc Brakes vs. Drum Brakes

For many years, drum brakes was the prevailing type of brake system used in automobiles. In the late 1960‘s and early 1970’s, many manufacturers started to switch from drum brakes to disc brakes, which are superior in a few ways.

The majority of stopping power comes from the front wheels, so initially manufacturers tended to install disc brakes in the front and drum brakes in the rear. Since then, a number of high-end performance automobiles switched over to all wheels having disc brakes. However, quite a few mid-range vehicles today still use the discs in front and drums in the rear model.

The two braking systems differ in how exactly they work, and consequently have different ways they break down or wear out. It’s useful to understand the difference between the two, since it’s somewhat likely that your vehicle has both disc and drum brakes.

A drum brake works by transferring braking energy into a round drum, which rotates along with the wheel. When the brake pedal is pressed, a set of brake shoes – made of a heat-resistant material – expand outward and press against the turning drum and slow down the wheel.

A disc brake, in contrast, uses a thin circular brake disc and a brake caliper to apply the friction, rather than a metal drum. When a disc brake system’s pedal is pressed, the brake caliper presses (together) from each side onto the brake rotor, with brake pads making the contact.

The reason disc brakes are superior to drum brakes is that when doing heavy braking significantly more heat can build up within the metal drum. This can ultimately cause the drum brake system to fade. Fading is when the brake pedal becomes spongy, something that’s usually caused by excess heat somewhere in the system. This typically happens in serious braking conditions, like trying to brake at high speeds when going downhill. By contrast, a disc brake is open and exposed to the air, and so heat doesn’t build up like it does in a drum brake.

While disc brakes are better in extreme conditions, drum brakes are considerably less expensive. For most people, a vehicle using front disc brakes and rear drum brakes strikes a good balance of economy and performance. Typically, higher performance vehicles are equipped with and are best served by four-wheel disc brakes.

This illustration shows the difference between disc brakes and drum brakes.

Maintenance of the Brake System
Having an understanding of how the brake system works is the first step toward understanding how brakes can wear out or break down. While brakes should generally last for a good long while with regular inspection and maintenance, there are some areas that tend to be the problematic if something should go wrong.

Knowing what those areas are and what possible signs of trouble are can give you an early warning so you can nip issues in the bud. You don’t want to end up in an unsafe situation due to underperforming brakes, where your brakes let you down at the worst possible moment. The following are some things to be aware of about the brake system and common issues.

Brake Pads and Brake Rotors

Brake pads are the heat-resistant friction material that presses against the brake rotors (brake discs) to slow the wheel in a disc brake system. Brake pads are designed to resist wear and damage from the immense heat and pressure being applied to them, but over time they will wear down and need to be replaced, much like your tires do.

The nice thing about disc brakes is that, on many cars, you can usually check yourself to see if your brake pads need replacement, at least the outer brake pads – without removing your wheels. You can look through the spokes or slots of the wheels to locate the metal brake rotor within the wheel. On the outer edge of the brake rotor is the brake caliper, and in between the brake rotor and brake caliper are the brake pads.

You should have at least a quarter-inch’s thickness for each brake pad. At or below that threshold, it’s probably time to come in and have us remove the wheels for a closer look and possibly get new brake pads. When you’re inspecting the brake pads, you should take a look at the brake rotor as well. If the brake rotor is smooth, most likely all is well. If there are deep grooves or pits in the brake rotor, though, it may be time to replace the brake rotor. Our professional brake inspection will include measuring the brake rotor thickness to be sure it is within manufacturer’s specifications.

Of course, there are some wheel structures that don’t let you inspect your brake pads from the outside, and it’s necessary to remove the wheels to check the brakes. If you have wheels like these, or if you’re not comfortable inspecting the brake pads yourself, you can always rely on us and bring your vehicle in for our Certified Automotive Experts to perform a free brake inspection.

In addition, you can keep an eye (or ear) out for the following additional signs that your brake pads or brake shoes might be worn out or damaged:

• If you hear a rotational screech while driving, this could be the indicator – a metal tab designed to come into contact with the brake rotor once the brake pad is worn out or worn out. That sound is telling you that your brake pads need replacement.
• If the car seems to pull either to the left or the right while you brake, there’s a possibility that one of the brake calipers has become stuck or is malfunctioning. When this happens, friction is applied unevenly, leading to the drift or pull in the opposite direction of the stuck brake caliper. You’ll need to have this inspected and repaired.
• If your car vibrates significantly when braking, there’s a chance that your brake rotors are warped or damaged. When the brake rotor is damaged, the brake pads rub unevenly against it, and that vibration travels through the car. The brake rotor will need to be resurfaced or replaced in this case.
• If the brake pedal seems ‘soft’ – in other words, you need to push almost down to the floor in order to apply the brakes – this could mean you have worn out brake pads or other more serious brake system issues. It also could mean that you have a leak or issue with one or more of the hydraulic brake components, and it’s imperative to get this checked out.

It’s worth noting that letting your brake pads wear down completely can be a costly mistake. When brake pads wear down too much, braking will cause the metal backing of the brake pads or, in some instances, the brake calipers to impact directly against the brake rotor. This is often referred to as worn metal-to metal. This can cause damage to both the brake calipers and the brake rotor, and both are significantly more expensive to replace than replacing just the brake pads. Staying on top of your brake pads’ condition can save you money in the long run. Thus, we recommend periodic brake inspections. If you service your vehicle regularly with us, rest assured that we inspect brakes in our shop at every maintenance interval.

Like with disc brakes, a decline in responsiveness or performance of the brakes can signal that your brake shoes need to be replaced. Another area often affected is the parking brake. When brake shoes are worn, the brake shoes can’t grip sufficiently on the brake drum and the parking brake may not be effective.

If you observe any of these things, it’s time for a brake inspection and you probably need new brake shoes.

Brake Fluid

As a hydraulic system, your brakes rely on the brake fluid, a type of hydraulic fluid,  in order to function properly. The brake fluid is compressed by the brake master cylinder’s piston to apply force to the brake caliper to slow your wheels, and if that brake fluid isn’t in good shape it’s not going to perform properly. The entire braking system is dependent on your brake fluid, and over time that fluid degrades.

The issue is that your brake fluid becomes contaminated by a number of impurities and moisture over thousands of miles of driving. Certain parts of the braking system, including the brake master cylinder, brake calipers, and brake wheel cylinders contain some rubber or plastic, and both of them degrade over time. Little by little, particles from that deterioration make their way into your brake fluid.

Another problem is getting water or other moisture into the braking system. This produces corrosion, and as that rust wears away it too makes its way into the fluid. Not to mention, the brake fluid itself wears out through constant compression, expansion, and pressure conditions within the hydraulic brake system.

At a certain point, your brake fluid isn’t up to the job of powering your brakes anymore, and you need to have a brake fluid flush. This is the process of removing all your brake fluid and replacing it with brand new fluid.

Brake fluid happens to be extremely toxic, and it’s best to bring your vehicle to our Certified Automotive Experts to have your brake fluid replaced. We recommend to have a brake fluid flush around every 30,000 miles or two years.

First of all, you’re not going to be perfect in detecting some of the less common problems with things like the thickness of your brake rotors or brake drums. You may be able to spot a very badly damaged brake rotor, for example, but a more subtly worn or damaged one, or one that’s worn under specification with no outward sign of damage requires measurement with a micrometer and may be beyond your ability to detect. Left undetected, you could end up driving until you do more significant damage to the braking system, or even worse run into a situation where your brakes aren’t fully responsive when you need them to be.

Beyond the parts of the braking system that you’re able to easily inspect yourself, there’s the entire rest of the system, which isn’t easily accessible. Leaks on hydraulic brake components or damage to your hydraulic fluid lines or hoses aren’t something you’re likely to be able to easily detect yourself. Any issues deeper in the braking system, like within the master cylinder, are similarly going to be beyond most do-it-yourselfer’s ability to check out.

Making sure you have un-worn brake pads is great, and you should definitely be monitoring that. But some parts of the braking system are complex, and the amount of heat, pressure, and friction it’s under on a routine basis means you will want a professional check-up periodically.

Brake Fluid

Always be diligent about brake system inspections and maintenance. After all, there are few things more important than being able to stop your vehicle at a moment’s notice. Trouble can happen on the road in the blink of an eye, and you absolutely want your brakes to be able to respond just as quickly as you do.